Conventionally, there has been frequently noted such a problem that thermoplastic resins used for an organic photoreceptor employed in electrophotographic image formation results in halftone nonuniformity due to surface scratches of the photoreceptor under an ambience of high temperature and humidity. As a method to solve this problem, improvements employing a photoreceptor provided with a protective layer have been attempted. Specifically, to increase surface hardness, there have also been conducted investigations on enhancement of strength of a protective layer via cross-linking reaction utilizing energy such as heat or light (Patent Document 1). In this manner, to enhance cross-link density by use of heat or light energy, there are various methods as described above, but from the viewpoint of the extent of cross-linking reaction, cross-linking reaction via light is suitable (Patent Document 2).
But cross-link density enhancement tends to easily impair potential characteristics. This reason has been thought to be that light energy required for cross-linking deteriorates the photosensitive layer.
However, in a cross-linking reaction system via light, when the amount of light to initiate curing reaction is decreased, the amount of generation of active species serving for the initiation point of the reaction is decreased, whereby photocuring inadequately proceeds, resulting in a protective layer with less strength. In contrast, with an excessive amount of light, curing adequately proceeds and then the strength of the protective layer is enhanced. However, excessive light also irradiates a photosensitive layer, which will be then deteriorated, resulting in insufficient potential stability over a print run of multiple sheets. Therefore, there has not always been compatibility of halftone nonuniformity due to surface scratches and potential stability over a print run of multiple sheets.
[Patent Document 1] Unexamined Japanese Patent Application Publication No. (hereinafter referred to as JP-A) 9-281736
[Patent Document 2] JP-A 2001-125297